User's Manual

July 23, 2002 B-3
CreataLink2 XT Hardware Integrator’s Guide Appendix B
Desense Overview
Noise Sources
CPU clocks, address and data buses, user displays, switching power supplies, and
peripheral drivers are sources of EMI. The frequency of these emissions is unstable
because high stability clock sources are not required in host computer designs. The
frequency of sources drifts as a function of temperature, time, and aging. The edges
of clock signals create detectable harmonics in the 1-GHz band and move in the
frequency spectrum as a function of time. To measure the effects of these emissions,
determine where the emissions exist in the frequency spectrum.
Noise from the host is conducted through the electrical/mechanical interface or
radiates electromagnetic fields received by the data transceiver antenna. Smart-
Synch, Inc. data transceivers are designed to minimize conducted noise.
Radiated electromagnetic fields from internal circuitry are incident on the data
transceiver antenna. These fields are converted to noise power via the antenna and
are incident on the receiver. Physical interface signaling has less impact on receiver
performance and can be electrically decoupled via passive components.
Receiver Susceptibilities
The receiver is susceptible to desense within the channel bandwidth and at
intermediate frequencies used for down-conversion. Excessive noise on power
supply pins can also create sensitivity problems.